The present inventive concept relates to nonvolatile memory devices which utilize a variable resistive element to store data.
Examples of a nonvolatile memory device that utilize variable resistance materials include phase change random access memory (PRAM), resistive RAM (RRAM), a magnetic RAM (MRAM), and the like. In contrast to dynamic RAM (DRAM) device and flash memory which store data according to an electric charge, variable resistance memory devices are characterized by storing data according to a programmable resistance of a variable resistance material. As examples, data may be stored according to a change in state of a phase change material (PRAM), such as a chalcogenide alloy, a change in resistance of a variable resistive material (RRAM), and a change in resistance of a magnetic tunnel junction (MTJ) thin film due to a magnetization state of a ferromagnetic substance (MRAM).
The description of embodiments described later herein use a phase change memory cell as an example. A state of a phase change material is changed to a crystal state or an amorphous state by controlling a heating process and subsequent cooling process applied to the material. Since the phase change material in the crystal state has low resistance and the phase change material in the amorphous state has high resistance, the crystal state may be defined as set data or 0 data, and the amorphous state may be defined as reset data or 1 data.